This invention relates to an electronic musical instrument and, more particularly, to an electronic musical instrument comprising a plurality of musical tone generator systems which are different from each other in the manner of producing musical tones and being capable of separately generating a musical tone designated by a key being depressed in the musical tone generator systems and simultaneously reproducing the musical tone from these different systems.
Various proposals have been made in the past for producing musical tones in an electronic musical instrument. These proposals include (1) a method for producing a musical tone by sequentially reading out, at a proper reading rate, a musical tone waveshape reviously stored in a memory device, as sampled values of the waveshape (2) a method for producing a musical tone waveshape by multiplying amplitude values of respective harmonic components constituting a musical tone with sinusoidal signals having frequencies of the respective harmonic components and thereafter adding the results of such multiplication together and (3) a method for producing a musical tone by applying a tone source signal containing abundant harmonic components to a filter and attenuating predetermined harmonic components for obtaining a desired tone color.
Each of the proposed methods has its own merits and advantages but a desirable musical tone cannot be produced by applying one of such methods individually to an electronic musical instrument. A natural musical tone is a result of combination of various factors including complicated combinations of a large number of harmonic components and change of such combinations in relation to time. A musical tone to be obtained by one of the above described methods is insufficient when compared with a natural musical tone. The above described method (1), for example, requires a large number of waveshape memories since a single constant tone color only is stored in each of such waveshape memories. Besides, the methods (1) and (2) are disadvantageous because such methods can hardly produce change in the tone color (i.e. harmonic components) occurring with a lapse of time. Further, the method (3) has a limitation the extent of the harmonic components available for use and therefore is unable to produce complicated combination of a large number of harmonic components. For these reasons, a perfect simulation of a natural musical tone has not been realized by the above described methods.
There is a type of electronic musical instrument called a music synthesizer which is an application of the above described method (3). This type of musical instrument in which signals are all processed in an analog circuit has difficulties in maintaining an accurate pitch of the musical tone frequency and also in designing it in IC configuration. Besides, the musical synthesizer is incapable of simultaneously reproducing a plurality of musical tones so that its application is limited to a monotone musical instrument.
Characteristics of voltage-controlled type variable filter (hereinafter referred to as VCF) and a voltage-controlled type variable gain amplifier (hereinafter referred to as VCA) which are both used in the above described music synthesizer can be varied as desired by varying the cut-off frequency (in VCF) amplification gain (in VCA) in accordance with a control voltage. These VCF and VCA have therefore been utilized in other types of electronic musical instruments for controlling tone color and volume of a musical tone. Since it is desirable in electronic musical instruments that tone color and volume should vary with the lapse of time, a waveshape which changes with the lapse of time is generally used as a control voltage to be applied to these VCF and VCA. Accordingly, this control voltage waveshape determines variation in the tone color and an envelope of level change.
The prior art electronic musical instruments have produced such control voltage by utilizing charge and discharge waveshapes of a capacitor or by sequentially reading out levels at respective sample points of an envelope waveshape previously stored in a memory. The method of using a capacitor, however, defective in that the envelope waveshape cannot be changed as desired. The method of using a memory also has a problem that a large number of sample points is required for achieving satisfactory resolution of an envelope waveshape and, accordingly, a memory of large capacity is required with a resulting increase in the manufacturing cost.